--- 1/draft-ietf-mboned-ieee802-mcast-problems-09.txt 2019-11-04 15:14:08.137626398 -0800 +++ 2/draft-ietf-mboned-ieee802-mcast-problems-10.txt 2019-11-04 15:14:08.189627714 -0800 @@ -1,54 +1,54 @@ Internet Area C. Perkins Internet-Draft Intended status: Informational M. McBride -Expires: March 29, 2020 Futurewei +Expires: May 7, 2020 Futurewei D. Stanley HPE W. Kumari Google JC. Zuniga SIGFOX - September 26, 2019 + November 4, 2019 Multicast Considerations over IEEE 802 Wireless Media - draft-ietf-mboned-ieee802-mcast-problems-09 + draft-ietf-mboned-ieee802-mcast-problems-10 Abstract Well-known issues with multicast have prevented the deployment of multicast in 802.11 and other local-area wireless environments. This document offers guidance on known limitations and problems with - wireless Layer-2 multicast. Also described are certain multicast - enhancement features that have been specified by the IETF and by IEEE - 802 for wireless media, as well as some operational choices that can - be taken to improve the performance of the network. Finally, some - recommendations are provided about the usage and combination of these - features and operational choices. + wireless (primarily 802.11) Layer-2 multicast. Also described are + certain multicast enhancement features that have been specified by + the IETF and by IEEE 802 for wireless media, as well as some + operational choices that can be taken to improve the performance of + the network. Finally, some recommendations are provided about the + usage and combination of these features and operational choices. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on March 29, 2020. + This Internet-Draft will expire on May 7, 2020. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -59,21 +59,21 @@ described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Identified multicast issues . . . . . . . . . . . . . . . . . 5 3.1. Issues at Layer 2 and Below . . . . . . . . . . . . . . . 5 3.1.1. Multicast reliability . . . . . . . . . . . . . . . . 5 3.1.2. Lower and Variable Data Rate . . . . . . . . . . . . 6 - 3.1.3. High Interference . . . . . . . . . . . . . . . . . . 7 + 3.1.3. Capacity and Impact on Interference . . . . . . . . . 7 3.1.4. Power-save Effects on Multicast . . . . . . . . . . . 7 3.2. Issues at Layer 3 and Above . . . . . . . . . . . . . . . 7 3.2.1. IPv4 issues . . . . . . . . . . . . . . . . . . . . . 8 3.2.2. IPv6 issues . . . . . . . . . . . . . . . . . . . . . 8 3.2.3. MLD issues . . . . . . . . . . . . . . . . . . . . . 9 3.2.4. Spurious Neighbor Discovery . . . . . . . . . . . . . 9 4. Multicast protocol optimizations . . . . . . . . . . . . . . 10 4.1. Proxy ARP in 802.11-2012 . . . . . . . . . . . . . . . . 10 4.2. IPv6 Address Registration and Proxy Neighbor Discovery . 11 4.3. Buffering to Improve Battery Life . . . . . . . . . . . . 12 @@ -90,46 +90,49 @@ 5.2. Mitigating Spurious Service Discovery Messages . . . . . 18 6. Multicast Considerations for Other Wireless Media . . . . . . 18 7. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 19 8. Discussion Items . . . . . . . . . . . . . . . . . . . . . . 19 9. Security Considerations . . . . . . . . . . . . . . . . . . . 20 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20 12. Informative References . . . . . . . . . . . . . . . . . . . 20 Appendix A. Changes in this draft between revisions 06 versus 07 24 Appendix B. Changes in this draft between revisions 05 versus 06 24 - Appendix C. Changes in this draft between revisions 04 versus 05 24 + Appendix C. Changes in this draft between revisions 04 versus 05 25 Appendix D. Changes in this draft between revisions 03 versus 04 25 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25 1. Introduction Well-known issues with multicast have prevented the deployment of multicast in 802.11 [dot11] and other local-area wireless environments, as described in [mc-props], [mc-prob-stmt]. Performance issues have been observed when multicast packet transmissions of IETF protocols are used over IEEE 802 wireless media. Even though enhancements for multicast transmissions have been designed at both IETF and IEEE 802, incompatibilities still exist between specifications, implementations and configuration choices. Many IETF protocols depend on multicast/broadcast for delivery of - control messages to multiple receivers. Multicast is used for - various purposes such as neighbor discovery, network flooding, - address resolution, as well minimizing media occupancy for the - transmission of data that is intended for multiple receivers. In - addition to protocol use of broadcast/multicast for control messages, - more applications, such as push to talk in hospitals, or video in - enterprises, universities, and homes, are sending multicast IP to end - user devices, which are increasingly using Wi-Fi for their - connectivity. + control messages to multiple receivers. Multicast allows sending + data to multiple interested recipients without the source needing to + send duplicate data to each recipient. With broadcast traffic, data + is sent to every device regardless of their interest in the data. + Multicast is used for various purposes such as neighbor discovery, + network flooding, address resolution, as well minimizing media + occupancy for the transmission of data that is intended for multiple + receivers. In addition to protocol use of broadcast/multicast for + control messages, more applications, such as push to talk in + hospitals, or video in enterprises, universities, and homes, are + sending multicast IP to end user devices, which are increasingly + using Wi-Fi for their connectivity. IETF protocols typically rely on network protocol layering in order to reduce or eliminate any dependence of higher level protocols on the specific nature of the MAC layer protocols or the physical media. In the case of multicast transmissions, higher level protocols have traditionally been designed as if transmitting a packet to an IP address had the same cost in interference and network media access, regardless of whether the destination IP address is a unicast address or a multicast or broadcast address. This model was reasonable for networks where the physical medium was wired, like Ethernet. @@ -163,21 +166,21 @@ needs to be provided in order to make them more reliable. IPv6 neighbor discovery saturating the Wi-Fi link is only part of the problem. Wi-Fi traffic classes may help. This document is intended to help make the determination about what problems should be solved by the IETF and what problems should be solved by the IEEE (see Section 8). This document details various problems caused by multicast transmission over wireless networks, including high packet error rates, no acknowledgements, and low data rate. It also explains some - enhancements that have been designed at the IETF and IEEE 802 to + enhancements that have been designed at the IETF and IEEE 802.11 to ameliorate the effects of multicast traffic. Recommendations are also provided to implementors about how to use and combine these enhancements. Some advice about the operational choices that can be taken is also included. It is likely that this document will also be considered relevant to designers of future IEEE wireless specifications. 2. Terminology This document uses the following definitions: @@ -219,23 +222,23 @@ 3.1. Issues at Layer 2 and Below In this section some of the issues related to the use of multicast transmissions over IEEE 802 wireless technologies are described. 3.1.1. Multicast reliability Multicast traffic is typically much less reliable than unicast traffic. Since multicast makes point-to-multipoint communications, multiple acknowledgements would be needed to guarantee reception at - all recipients. Since typically there are no ACKs for multicast - packets, it is not possible for the Access Point (AP) to know whether - or not a retransmission is needed. Even in the wired Internet, this + all recipients. Since there are no ACKs for multicast packets, it is + not possible for the Access Point (AP) to know whether or not a + retransmission is needed. Even in the wired Internet, this characteristic often causes undesirably high error rates. This has contributed to the relatively slow uptake of multicast applications even though the protocols have long been available. The situation for wireless links is much worse, and is quite sensitive to the presence of background traffic. Consequently, there can be a high packet error rate (PER) due to lack of retransmission, and because the sender never backs off. It is not uncommon for there to be a packet loss rate of 5% or more, which is particularly troublesome for video and other environments where high data rates and high reliability are required. @@ -250,47 +253,48 @@ impact the ability for QoS solutions to effectively reserve bandwidth and provide admission control. For wireless stations associated with an Access Point, the power necessary for good reception can vary from station to station. For unicast, the goal is to minimize power requirements while maximizing the data rate to the destination. For multicast, the goal is simply to maximize the number of receivers that will correctly receive the multicast packet; generally the Access Point has to use a much lower data rate at a power level high enough for even the farthest station - to receive the packet, for example as briefly mentioned in [RFC5757]. - Consequently, the data rate of a video stream, for instance, would be - constrained by the environmental considerations of the least reliable - receiver associated with the Access Point. + to receive the packet, for example as briefly mentioned in section 2 + of [RFC5757]. Consequently, the data rate of a video stream, for + instance, would be constrained by the environmental considerations of + the least reliable receiver associated with the Access Point. Because more robust modulation and coding schemes (MCSs) have longer range but also lower data rate, multicast / broadcast traffic is generally transmitted at the slowest rate of all the connected devices. This is also known as the basic rate. The amount of additional interference depends on the specific wireless technology. In fact, backward compatibility and multi-stream implementations mean that the maximum unicast rates are currently up to a few Gbps, so there can be more than 3 orders of magnitude difference in the transmission rate between multicast / broadcast versus optimal unicast forwarding. Some techiques employed to increase spectral - efficiency, such as spatial multiplexing in mimo systems, are not - available with more than one intended reciever; it is not the case + efficiency, such as spatial multiplexing in MIMO systems, are not + available with more than one intended receiver; it is not the case that backwards compatibility is the only factor responsible for lower multicast transmission rates. Wired multicast also affects wireless LANs when the AP extends the wired segment; in that case, multicast / broadcast frames on the - wired LAN side are copied to WLAN. Since broadcast messages are - transmitted at the most robust MCS, many large frames are sent at a - slow rate over the air. + wired LAN side are copied to the Wireless Local Area Network (WLAN). -3.1.3. High Interference + Since broadcast messages are transmitted at the most robust MCS, many + large frames are sent at a slow rate over the air. + +3.1.3. Capacity and Impact on Interference Transmissions at a lower rate require longer occupancy of the wireless medium and thus take away from the airtime of other communications and degrade the overall capacity. Furthermore, transmission at higher power, as is required to reach all multicast STAs associated to the AP, proportionately increases the area of interference. 3.1.4. Power-save Effects on Multicast @@ -331,40 +335,41 @@ o On-demand routing o Backbone construction o Other L3 protocols (non-IP) User Datagram Protocol (UDP) is the most common transport layer protocol for multicast applications. By itself, UDP is not reliable -- messages may be lost or delivered out of order. 3.2.1. IPv4 issues - The following list contains some representative multicast protocols + The following list contains some representative discovery protocols that are used with IPv4. o ARP o DHCP o mDNS [RFC6762] o uPnP [RFC6970] After initial configuration, ARP and DHCP occur much less commonly, but service discovery can occur at any time. Some widely-deployed service discovery protocols (e.g., for finding a printer) utilize mDNS (i.e., multicast). It's often the first service that operators drop. Even if multicast snooping is utilized, many devices can register at once and cause serious network degradation. 3.2.2. IPv6 issues IPv6 makes extensive use of multicast, including the following: o DHCPv6 + o Protocol Independent Multicast (PIM) o IPv6 Neighbor Discovery Protocol (NDP) [RFC4861] o multicast DNS (mDNS) o Route Discovery o Decentralized Address Assignment o Geographic routing IPv6 NDP Neighbor Solicitation (NS) messages used in Duplicate Address Detection (DAD) and Address Lookup make use of Link-Scope multicast. In contrast to IPv4, an IPv6 node will typically use multiple addresses, and may change them often for privacy reasons. @@ -444,22 +449,22 @@ 4. Multicast protocol optimizations This section lists some optimizations that have been specified in IEEE 802 and IETF that are aimed at reducing or eliminating the issues discussed in Section 3. 4.1. Proxy ARP in 802.11-2012 The AP knows the MAC address and IP address for all associated STAs. In this way, the AP acts as the central "manager" for all the 802.11 - STAs in its BSS. Proxy ARP is easy to implement at the AP, and - offers the following advantages: + STAs in its basic service set (BSS). Proxy ARP is easy to implement + at the AP, and offers the following advantages: o Reduced broadcast traffic (transmitted at low MCS) on the wireless medium o STA benefits from extended power save in sleep mode, as ARP requests for STA's IP address are handled instead by the AP. o ARP frames are kept off the wireless medium. o No changes are needed to STA implementation. Here is the specification language as described in clause 10.23.13 of [dot11-proxyarp]: @@ -488,24 +493,24 @@ The 6lo Working Group has specified an update [RFC8505] to RFC6775. Wireless devices can register their address to a Backbone Router [I-D.ietf-6lo-backbone-router], which proxies for the registered addresses with the IPv6 NDP running on a high speed aggregating backbone. The update also enables a proxy registration mechanism on behalf of the registered node, e.g. by a 6LoWPAN router to which the mobile node is attached. The general idea behind the backbone router concept is that broadcast and multicast messaging should be tightly controlled in a variety of - Wireless Local Area Networks (WLANs) and Wireless Personal Area - Networks (WPANs). Connectivity to a particular link that provides - the subnet should be left to Layer-3. The model for the Backbone - Router operation is represented in Figure 1. + WLANs and Wireless Personal Area Networks (WPANs). Connectivity to a + particular link that provides the subnet should be left to Layer-3. + The model for the Backbone Router operation is represented in + Figure 1. | +-----+ | | Gateway (default) router | | +-----+ | | Backbone Link +--------------------+------------------+ | | | @@ -835,21 +840,21 @@ Similar considerations hold for most other wireless media. A brief introduction is provided in [RFC5757] for the following: o 802.16 WIMAX o 3GPP/3GPP2 o DVB-H / DVB-IPDC o TV Broadcast and Satellite Networks 7. Recommendations - This section will provide some recommendations about the usage and + This section provides some recommendations about the usage and combinations of the multicast enhancements described in Section 4 and Section 5. Future protocol documents utilizing multicast signaling should be carefully scrutinized if the protocol is likely to be used over wireless media. Proxy methods should be encouraged to conserve network bandwidth and power utilization by low-power devices. The device can use a unicast message to its proxy, and then the proxy can take care of any needed @@ -858,49 +863,57 @@ Multicast signaling for wireless devices should be done in a way compatible with low duty-cycle operation. 8. Discussion Items This section suggests two discussion items for further resolution. The IETF should determine guidelines by which it may be decided that multicast packets are to be sent wired. For example, 802.1ak works on ethernet and Wi-Fi. 802.1ak has been pulled into 802.1Q as of - 802.1Q-2011. 802.1Q-2014 can be found here: - http://www.ieee802.org/1/pages/802.1Q-2014.html. If a generic - solution is not found, guidelines for multicast over Wi-Fi should be - established. + 802.1Q-2011. If a generic solution is not found, guidelines for + multicast over Wi-Fi should be established. Reliable registration to Layer-2 multicast groups and a reliable multicast operation at Layer-2 might provide a generic solution. There is no need to support 2^24 groups to get solicited node multicast working: it is possible to simply select a number of trailing bits that make sense for a given network size to limit the number of unwanted deliveries to reasonable levels. IEEE 802.1, 802.11, and 802.15 should be encouraged to revisit L2 multicast issues. In reality, Wi-Fi provides a broadcast service, not a multicast service. On the physical medium, all frames are broadcast except in very unusual cases in which special beamforming transmitters are used. Unicast offers the advantage of being much faster (2 orders of magnitude) and much more reliable (L2 ARQ). 9. Security Considerations This document does not introduce or modify any security mechanisms. + Multicast is made more secure in a variety of ways. [RFC4601], for + instance, mandates the use of IPsec to ensure authentication of the + link-local messages in the Protocol Independent Multicast - Sparse + Mode (PIM-SM) routing protocol. [RFC5796]specifies mechanisms to + authenticate the PIM-SM link-local messages using the IP security + (IPsec) Encapsulating Security Payload (ESP) or (optionally) the + Authentication Header (AH). As noted in [group_key], the unreliable nature of multicast transmission over wireless media can cause subtle problems with - multicast group key management and updates. Quoting from that - website, "... most clients are able to get connected and surf the - web, check email, etc. even when From DS multicasts are broken. So a - lot of people don't realize they have multicast problems on their - network..." + multicast group key management and updates. When WPA (TKIP) or WPA2 + (AES-CCMP) encryption is in use, AP to client (From DS) multicasts + have to be encrypted with a separate encryption key that is known to + all of the clients (this is called the Group Key). Quoting further + from that website, "... most clients are able to get connected and + surf the web, check email, etc. even when From DS multicasts are + broken. So a lot of people don't realize they have multicast + problems on their network..." 10. IANA Considerations This document does not request any IANA actions. 11. Acknowledgements This document has benefitted from discussions with the following people, in alphabetical order: Mikael Abrahamsson, Bill Atwood, Stuart Cheshire, Donald Eastlake, Toerless Eckert, Jake Holland, Joel @@ -942,43 +955,42 @@ [dot11-proxyarp] Hiertz, G., Mestanov, F., and B. Hart, "Proxy ARP in 802.11ax", September 2015, . [dot11aa] "IEEE 802 Wireless", "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 2: MAC Enhancements for Robust Audio Video Streaming", March 2012, - . + . [group_key] - Spiff, ""Why do some WiFi routers block multicast packets - going from wired to wireless?"", Jan 2017, + Spiff, "Why do some WiFi routers block multicast packets + going from wired to wireless?", Jan 2017, . [I-D.ietf-6lo-backbone-router] Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6 Backbone Router", draft-ietf-6lo-backbone-router-13 (work in progress), September 2019. [I-D.ietf-6tisch-architecture] Thubert, P., "An Architecture for IPv6 over the TSCH mode - of IEEE 802.15.4", draft-ietf-6tisch-architecture-26 (work - in progress), August 2019. + of IEEE 802.15.4", draft-ietf-6tisch-architecture-28 (work + in progress), October 2019. [I-D.ietf-mboned-driad-amt-discovery] Holland, J., "DNS Reverse IP AMT Discovery", draft-ietf- - mboned-driad-amt-discovery-08 (work in progress), June + mboned-driad-amt-discovery-09 (work in progress), October 2019. [ietf_802-11] Stanley, D., "IEEE 802.11 multicast capabilities", Nov 2015, . [mc-ack-mux] Tanaka, Y., Sakai, E., Morioka, Y., Mori, M., Hiertz, G., @@ -1010,35 +1022,47 @@ Discovery for IP Version 6 (IPv6)", RFC 2461, DOI 10.17487/RFC2461, December 1998, . [RFC4541] Christensen, M., Kimball, K., and F. Solensky, "Considerations for Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Snooping Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, . + [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, + "Protocol Independent Multicast - Sparse Mode (PIM-SM): + Protocol Specification (Revised)", RFC 4601, + DOI 10.17487/RFC4601, August 2006, + . + [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, DOI 10.17487/RFC4861, September 2007, . [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, DOI 10.17487/RFC4862, September 2007, . [RFC5757] Schmidt, T., Waehlisch, M., and G. Fairhurst, "Multicast Mobility in Mobile IP Version 6 (MIPv6): Problem Statement and Brief Survey", RFC 5757, DOI 10.17487/RFC5757, February 2010, . + [RFC5796] Atwood, W., Islam, S., and M. Siami, "Authentication and + Confidentiality in Protocol Independent Multicast Sparse + Mode (PIM-SM) Link-Local Messages", RFC 5796, + DOI 10.17487/RFC5796, March 2010, + . + [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, DOI 10.17487/RFC6282, September 2011, . [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, DOI 10.17487/RFC6762, February 2013, . [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service